Hereford cows were randomly bred to Hereford, Angus, Simmental X Hereford and Simmental sires. Each sire breed group was represented by nine or 10 sires. These matings produced approximately 100 calves in each sire breed group over 4 yr. The objective of this study was to determine the effect of calf breed on characteristics of the cow such as milk production, reproduction, measures of condition, weight and changes in condition and weight during lactation. All of the cows were contemporary Herefords that were raised and managed under similar environmental conditions. Hence, any detection of an important effect of calf breed on cow productivity should be a reflection of different levels of maternal requirement imposed on the cow by the different calf breed groups. Cows that raised crossbred calves gained less weight from precalving to weaning, had lower condition scores at weaning, had smaller gains in weight change per unit of height and experienced a lower pregnancy rate. All results consistently showed that crossbred calves challenged the maternal ability of their dams to a greater degree than the straightbred calves and that among the crossbred calves, those by Simmental sires challenged their dams the most. It appeared that calf breed group effects on cow traits were at least partially mediated through calf growth rate, but not through parturition stress. Therefore, benefits realized from crossbreeding need to be weighted against possible unfavorable results.